1. Field of the Invention
This invention relates to a double-side optical disc having a recording surface for information signals on each side thereof and, more particularly, to a double-side optical disc composed of a pair of optical discs each having a signal recording surface on one side thereof and bonded to each other by an adhesive.
2. Description of the Prior Art
There has been proposed an optical disc in which data signals in the form of pits are formed by resin molding using a stamper and subsequently read out by an optical pickup.
The optical disc is constituted by a disc-shaped base material formed of a synthetic resin, such as polycarbonate, acrylic resin or epoxy resin, or glass, and a signal recording layer of, for example, a magnetic material, formed on the major surface of the disc shaped base material.
As such optical disc, there has been proposed a double-side optical disc 102 comprised of a pair of optical disc halves 101a, 101b bonded to each other as shown in FIG. 1 to enable data signals to be read and/or written from or on both major surfaces of the disc. The optical disc halves 101a, 101b of the double-side optical disc 102 are bonded together at the back sides thereof so that the front sides on the signal recording sides face to outside. The optical disc halves 101a, 101b are bonded together by applying an adhesive 103 of, for example, a rubber material, on the overall back sides thereof and pressing the disc halves together in the superimposed state.
Meanwhile, when the adhesive 103 is applied on the optical disc halves 101a, 101b for producing the double-side optical disc 102, the surface of the adhesive 103 tends present irregularities. It is because the adhesive 103 is applied by roll coating in which the adhesive is applied to the outer periphery of a rotating applicator roll and by bringing the applicator roll into rolling contact with the optical discs 101a, 101b.
Should the surface of the adhesive 103 present irregularities, the optical disc halves 101a, 101b bonded together tend to deviate from optimum smoothness due to the surface irregularities of the adhesive 103. Unless the smoothness of the optical discs 101a, 101b is maintained, the signal recording layer is deteriorated in flatness to render it difficult to write and/or read data signals on or from the signal recording layer under optimum states.